A photosensitive composition is a composition in which a photopolymerization initiator is added to a polymerizable compound having (an) ethylenic unsaturated bond(s). Since the photosensitive composition can be cured through polymerization on irradiation with 405-nm or 365-nm light, it is used for photocurable inks, photosensitive plates, various types of photoresists, and the like. Since a photosensitive composition sensitive to a shorter wavelength light source facilitates printing at higher resolution, there has been demand for a photopolymerization initiator with particularly high sensitivity to a 365-nm light source.
Patent Document 1 below proposed the use of an oxime ester derivative as a photopolymerization initiator used in such a photosensitive composition, and Patent Documents 2 to 4 below also described oxime ester compounds. When any of these publicly known oxime ester compounds was used as a photopolymerization initiator, however, decomposition products which generated on exposure attached to a mask, causing fault in the pattern shape on printing, and hence lowering the yield. In addition, since these oxime ester compounds have a decomposition temperature of 240° C. or lower, the photopolymerization initiator may decompose in a post-development thermosetting treatment which is typically performed at 130 to 240° C., possibly deteriorating properties of the resultant resin. For this reason, the thermosetting treatment was required to be performed at lower temperature for a long duration. Although thermosetting treatment at higher temperatures could shorten the duration of treatment, the properties of resins would be deteriorated by heat. Thus, in thermosetting treatment at higher temperatures, a photopolymerization initiator with higher heat resistance is required. It has been, therefore, desired a photopolymerization initiator with a decomposition temperature of 240° C. or higher that causes neither coloration of the resultant polymerized material nor generation of decomposition products that may diffuse as vapor and contaminate the polymerized material, apparatuses, or the like.
Patent Documents 5 to 8 below proposed O-acyloxime photopolymerization initiators with higher reactivity. These O-acyloxime photopolymerization initiators, however, were still unsatisfactory in terms of sensitivity, and a more sensitive photopolymerization initiator has been desired. Patent Document 7 below disclosed an O-acyloxime compound having a carbazolyl moiety, but that compound was not satisfactory in terms of sensitivity, resolution, or alkali resistance either.    Patent Document 1: U.S. Pat. No. 3,558,309    Patent Document 2: U.S. Pat. No. 4,255,513    Patent Document 3: U.S. Pat. No. 4,590,145    Patent Document 4: U.S. Pat. No. 4,202,697    Patent Document 5: JP-A-2000-80068    Patent Document 6: JP-A-2001-233842    Patent Document 7: WO 02/100903    Patent Document 8: WO 2004/050653